intermittent code P0300

I am having intermittent p0300. Only really noticeable at idle and like I said it's intermittent. To the point the code will clear after enough ignition cycles. I have already replaced all the lifters, cam was in good condition, the VLOM, oil pressure sensor, MAP sensor, injector on 6, plugs, wires, cleaned throttle body, cleaned the MAF, had the heads gone over and milled .03, the wiring loom/harness is in decent shape. I will also get a p0306. (the reason I replaced injector) to no avail. The service stabilitrak, and service traction control will kick on at idle. If I raise the RPMs and hold it it will go away with no check engine some times. If I don't raise RPMs it will begin to miss harder to the point the check engine light flashes. Oil pressure is decent but could be a little better, never lower than 30, never higher than 58 or so. What should I load into the parts cannon next?!?